Steam-heated and induction-heated rollers are used in the paper making, printing, paper, film, and foil converting industries. Some examples are: web heating rollers, drying rollers and drums, laminating rollers, embossing rollers, and cast film extrusion rollers.
Steam-heated rollers act as pressure vessels at higher temperatures. The internal construction of both steam-heated and induction-heated cores can be quite complex and expensive in order to provide the temperature uniformity needed. In addition, a considerable amount of auxiliary equipment is needed to power or heat the roller.
Internally heated fuser rollers are used in the copier industry. The fuser roller melts the toner and presses it into the paper. The typical fuser roller consists of an aluminum or non-magnetic metal core with an internal quartz heating lamp. The inner diameter of the core has a special coating to absorb heat from the lamp. The roller is coated with a non-stick elastomeric material (e.g., silicone rubber) to provide a pressure nip with an opposing roller and to release the toner to the paper.
The core construction is quite complex and expensive. The quartz lamp is fragile, has a limited useful life, and does not provide a uniform temperature distribution to the core.
A technical problem in the technology is the non-uniform temperature across the roller face when the width of the paper sheet or web is smaller than the heated length of the roller. The ends of the roller operate at a higher temperature than the portion covered by paper or sheet or web, which tends to dissipate heat from the covered portion of the roller. The higher temperature at the ends causes increased aging if the outermost covering is organic.
Heating rollers for xerography and other applications with multiple heating elements are disclosed in the following U.S. Patents, Sakurai, et al., U.S. Pat. No. 4,618,240; Kogure, et al., U.S. Pat. No. 4,801,968; Martin, et al., U.S. Pat. No. 4,883,941; Hager, U.S. Pat. No. 3,310,655, and d'Hondt, et al., U.S. Pat. No. 5,041,718.
It is typical in heater rollers to apply a voltage potential at one end of the heating layer and a ground potential at the other end of the heating layer to produce a current in the heating layer.
For example, in Satomura, U.S. Pat. No. 4,628,183, one side of a voltage supply is applied to one set of conductive fingers in a ceramic heating layer, while the other side of the voltage supply is applied to another set of conductive fingers in the ceramic heating layer. The two sets of fingers are interdigitated and electrical current is produced in the heating layer between the two sets of fingers.
The ceramic material is a baked ceramic material in which the conductive electrodes are sandwiched between two ceramic layers.
The present invention is directed to improved constructions of heater rollers for zone heating of a ceramic, resistive heating layer.